A mass balancing unit having one or more balancing shafts has the purpose of compensating for the inertia forces and/or moments of inertia which typically occur in an internal combustion engine. To this end, at least one balancing weight is provided, in particular mounted in a rotationally secure manner, on the respective balancing shaft in order to form an unbalanced mass. The balancing shaft is drivingly connected to the crankshaft of the internal combustion engine, whereby the balancing shaft and the balancing weight which is provided thereon are caused to rotate. In specific engine types, for example, in in-line engines having four cylinders, such balancing shafts are used in pairs, the balancing shafts rotating in opposing directions. In other engine types, there is provided a single balancing shaft which has, for example, two balancing weights which are arranged in a diametrically opposed manner relative to each other but in an axially offset manner.
Owing to the use of roller bearings, particularly quiet running of the respective balancing shaft is achieved and high speeds can be reached. With an integral longitudinal portion of the balancing shaft forming an inner bearing ring of the roller bearing, the structure of the roller bearing is simplified. If the balancing shaft is hollow, it also has an advantageously low weight and moment of inertia.
Owing to the unbalanced mass brought about by the balancing weight, however, the balancing shaft and the bearings thereof are heavily loaded so that a correspondingly stable construction of the shaft and sizing of the bearings are required. However, this leads to a great weight and undesirably high costs for the mass balancing unit.